The present invention relates to a chip-type multi-layer electronic part having internal electrodes, and particularly relates to the composition of the terminal electrodes.
In a chip-type multi-layered electronic part, for example, in a multi-layered chip capacitor, generally a plurality of ceramic green sheets provided with an internal electrode of nickel, copper, silver, silver/palladium, or the like are laminated and baked so as to form a capacitor chip 2 constituted by a dielectric laminated body including internal electrodes 1, as shown in FIG. 2. Terminal electrodes 3 containing copper, silver or silver/palladium alloy as their main ingredients and having electrical conduction to the internal electrodes 1 are formed in both end portions of the chip 2 by baking or the like. After that, a nickel layer 3a and a tin or tin alloy layer 3b are provided by electrolytic plating. The chip-type multi-layered electronic part configured thus is joined with a land 5 on a substrate 4 through solder or conductive resin 6.
In the chip-type multi-layered electronic part shown in FIG. 2, there is a problem that the surface of the terminal electrodes 3 is oxidized easily by heating when the chip-type multi-layered electronic part is joined with the substrate 4 through the conductive resin 6, so that failure in conduction is caused by the oxidization. In addition, there is a problem that if the internal electrodes 1 is made of base metal such as nickel, copper or the like, they are apt to be oxidized when the terminal electrodes 3 are formed by baking or the like, and failure in conduction occurs easily.
Taking the foregoing problems into consideration, it is an object of the present invention to provide a chip-type multi-layered electronic part in which terminal electrodes are prevented from oxidization when the terminal electrodes are joined with a substrate by heating, so that superior electrical bonding with internal electrodes can be attained.
In addition, it is another object of the present invention to provide a chip-type multi-layered electronic part in which the internal electrodes are prevented from oxidization when the terminal electrodes are formed, so that superior electrical bonding between the terminal electrodes and the internal electrodes can be attained.
According to the present invention, there is provided a chip-type multi-layered electronic part comprising: internal electrodes each of which is made of metal; and terminal electrodes suitably connected to the internal electrodes, each of the terminal electrodes containing silver and palladium as main ingredients thereof in a weight ratio in a range of from 7:3 to 3:7, and further containing boron in a range of from 0.1 weight percent to 1.0 weight percent added to the main ingredients of 100 weight percent.
By making the terminal electrodes have such composition, lead-out portions of the internal electrodes are prevented from oxidization when the terminal electrodes are baked, so that the contact between the terminal electrodes and the lead-out electrodes, can be kept satisfactory.
In addition, the terminal electrodes are prevented from oxidization, so that it is possible to prevent increase in resistance values of the terminal electrode portions and the internal electrodes, and it is possible to prevent deterioration in electrical characteristics, such as reduction in Q-value or the like, due to the increase in those resistance values. When the percentage of palladium is smaller than the above-mentioned silver/palladium weight ratio of 7:3, there arises failure in joining between the internal electrodes and the terminal electrodes. On the contrary, when the percentage of palladium is larger than the above-mentioned weight ratio of 7:3, there appears oxidization in the terminal electrodes, thereby causing the above-mentioned deterioration in electrical characteristics.
When the loading of boron is less than 0.1 weight percent, the effect of adding boron cannot be expected so much and the internal electrodes are apt to be oxidized. On the contrary, when the loading of boron exceeds 1.0 weight percent, baking the terminal electrodes is blocked so that the internal electrodes are apt to be oxidized.
According to the invention, preferably, the internal electrodes is made of nickel. When the internal electrodes is made of nickel, the present invention can exert a more valid effect in the sense of preventing the internal electrodes from oxidization when the terminal electrodes are formed and when the terminal electrodes are heated and attached to a substrate.
Preferably, each of the terminal electrodes has a one-layer structure having no surface plated layer.
If the terminal electrodes are made thus to have a one-layer structure, it is possible to restrain the terminal electrodes from oxidization when they are joined through conductive resin, so that it is possible to make them suitable for mounting the chip-type multi-layered electronic part on a substrate through the conductive resin.